Arbuscular Mycorrhizal Fungi Mediate Grazing Effects on Seasonal Soil Nitrogen Fluxes in a Steppe Ecosystem
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Arbuscular Mycorrhizal Fungi Mediate Grazing Effects on Seasonal Soil Nitrogen Fluxes in a Steppe Ecosystem Bo Tang,1,2 Jing Man,1,2 Ruoyu Jia,1,2 Yang Wang,1 and Yongfei Bai1,3* 1
State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Beijing 100093, China; 2College of Life Sciences, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, China; 3College of Resources and Environment, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, China
ABSTRACT Grazing and arbuscular mycorrhizal fungi (AMF) influence soil nitrogen (N) cycling in grassland ecosystems. However, it remains unclear whether AMF mediate grazing effects on soil N cycling. We investigated the influence of benomyl (a broadrange fungicide) application to suppress AMF on soil N fluxes under different levels of grazing intensity in a steppe ecosystem on the Mongolia plateau. In situ soil core incubation method was used during both growing and non-growing seasons. Benomyl application to suppress AMF remarkably stimulated the net nitrification rate across all grazing intensities during the growing season. Benomyl application exerted a negative effect on soil N fluxes and/or N pools under no to moderate levels of grazing and a positive effect under heavy grazing during the growing season. The responses of amino acid and inorganic N stocks to grazing differed substantially between growing
and non-growing seasons. The accumulation of amino acid in grazed plots (especially heavily grazed plots) during the non-growing season enhances the substrate availability for microbes in the early growing season of the following year. Our study provides field evidence that N losses are controlled to some extent by AMF and suggests a mechanism that grazing may affect soil N cycling through changing the AMF-plant symbiosis and therefore the interactions between AMF and other microbes. The findings improve our understanding of the effects of grazing and AMF on seasonal dynamics of different N forms and N pools in semiarid grassland. Key words: grazing intensity; benomyl application; arbuscular mycorrhizal fungi (AMF) suppression; N forms and N pools; amino acids; growing season vs. non-growing season.
Received 30 November 2019; accepted 29 September 2020 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-020-00575-8) contains supplementary material, which is available to authorized users. Author Contributions YB conceived the study; BT conducted the experimental treatment and field sampling; BT and JM conducted the laboratory analysis; BT, JM, RJ, YW and YB analyzed the data and contributed to the manuscript writing. *Corresponding author; e-mail: [email protected]
INTRODUCTION Arbuscular mycorrhizal fungi (AMF), members of the fungal phylum Mucoromycota, are found to form symbiotic associations (that is, AM symbiosis) with roots of the vast majority of terrestrial plant species (Spatafora
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